This invention relates to tufting machine gauge parts, and more particularly to gauge part mounting blocks for mounting the hooks and knives in a tufting machine.
In the production of tufted pile fabric each reciprocating needle cooperates with a looper or hook which seizes a loop of yarn from the needle and releases the loop to form loop pile fabric or holds the loop until it is cut by a knife acting in scissors-like fashion against the side of the hook to form cut pile fabric. The gauge of the pile fabric is determined by the spacing between adjacent gauge parts, i.e., the needles, hooks and knives, of the tufting machine. In conventional tufting machines the loopers or hooks are mounted within corresponding slots cut in a looper or hook bar and secured therein by set screws threaded into the slot and into abutment with the shank of the looper or hook. The screw acts to force a reference surface of the looper or hook against the solid portion of the bar at the closed end of the slot. Such constructions are well known and extensively disclosed in the prior art and may best be illustrated in U.S. Pat. Nos. 3,064,600 and 3,595,184. This conventional mounting of the hooks creates difficulties in aligning closely spaced hooks and minimizing deflection thereof. Moreover, since the securing set screws are within the slots they have a minimal amount of hook bar material into which they are threaded thereby creating a weakness in the securing of the hooks to the bar. The end of the screw that engages the hook further places a burr on the cooperating edge of the hook which makes it difficult to remove the hook from the slot when replacement is required.
More recently, in tufting machines in which the gauge, i.e., the spacing between adjacent gauge parts, is less than 0.1 inch, modules in which the hook shanks are embedded by molding in a common modular body member in side-by-side disposition have been utilized with great success. Such construction substantially eliminates the difficulties of aligning hooks in the hook bar of the tufting machine since the hooks are aligned in a jig during the formation of the module and each body member has at least one alignment surface for clamping the module to the hook bar. One difficulty with this construction is that when one hook is worn or broken the entire module must be removed and, although procedures have been developed for extracting and replacing a worn hook, the module including the good hooks generally are discarded or returned for remanufacture. For fine gauge machines, such as 1/16 of an inch and smaller this problem is justified by the advantages provided by the modules, not the least of which is the precision of aligning the hooks and the reduced deflection of the hooks due to the pressure of the respective knives acting against a face thereof. However, for courser gauges, this justification is reduced.
Additionally, in conventional cut pile tufting machines the knives are mounted in knife blocks which in turn are mounted in a knife bar. The conventional knife blocks have two or more elongated channels within which the knives are mounted, and the block includes a cylindrical spigot extending from the body thereof for insertion within a bore formed in the knife bar as illustrated for example, in U.S. Pat. No. 3,084,645. Since the knives must act against the face of the respective hooks in scissors-like fashion with sufficient pressure, the knife block is pivoted within the bore to engage the face of the hook at an angle of inclination generally approximately 8.degree. and contact the hook at an angle of canter generally approximating 4.degree.. This latter angle is provided by cutting the bore in the knife bar at the canter angle. The combination of the angle of inclination and the angle of canter provides a compound angle to the knives relative to the hooks. Although the canter angle is effectively fixed by the angle of the bore, the angle of inclination of the block can become misaligned or can be incorrectly adjusted when the tufting machine is assembled or when a knife or knife block is replaced. Moreover, although the use of screws acting directly on the edges of each knife to secure the knives in the channels has been discarded for saddles such as that illustrated in U.S. Pat. No. 4,211,176, and other clamping members such as illustrated in U.S. Pat. No. 4,289,082, many problems still exist in relation to securing the knives within the channels.
To eliminate these deficiencies in fine gauge tufting machines the knives are embedded by molding within modular body members having alignment surfaces in a manner similar to that of the modular hooks. Thus, the correct compound angle is fixed and the knives are secured in their proper relationship. Although this is advantageous to all tufting machines, the same difficulty as that of the hook modules is presented, that is, an entire module must be replaced when a single knife is worn or broken. Again, for fine gauge tufting machines this modular construction is justified since space is a minimum, but for courser gauge machines the disadvantage of not being able to remove a single knife is undesirable.